Create a dialog box with QDesigner

Regards I am working with QDesigner to create a simple dialog box, as yet not allocate space to create the effect you want. I want to create a dialog box divided into two parts, where the first occupy at least two thirds of the area of the dialog box and the second the remaining space (at most one-third). In each of the two areas I want to put a QGroupBox empty, alone with his title. I’ve been testing with QHBoxLayout, QVBoxLayout and QGridLayout, but I can not do exactly what I want, the space of the dialog box always halved. My thanks in advance to who can give me some advice or suggestion.